Prediction of NLO response of substituted organoimido hexamolybedate: First theoretical framework based on p-anisidine adduct [Mo₆O₁₈(p-MeOC₆H₄N)]^2-

The second-order nonlinear optical (NLO) responses and dipole polarizabilities of p-anisidine adduct (imido derivative of hexamolybdates/polyoxometalates/POMs/Cluster) are studied by means of time dependent density functional (TDDFT) calculations. A substantial molecular second-order NLO response has been noticed in these organic-inorganic hybrid compounds, particularly [Mo₆O₁₇ cis-(p-MeOC₆H₄N)₂]²⁻ (system 2) and [Mo₆O₁₈ p-MeOC₆H₄N]^2- (system 1) having static second-order polarizability (β_vec) calculated to be 1949.60 au and 1565.10 au respectively. Both p-anisidine and cis-(p-anisidine) are found to be preferred choice over the trans-(p-anisidine) adduct. There is a fair probability for these systems to be selected as efficient second-order nonlinear optical materials. The movement of charge transfer from p-anisidine to hexamolybdate cluster (D–A) along the y-axis suggests molybdenum cluster acts as an acceptor (A) whereas p-anisidine working as a donor (D) in all the studied systems which is responsible for NLO response in such adducts. An incremental increase in the computed β_vec values were evaluated by incorporation of an electron donor (Metalloporphyrin) instead of p-anisidine. Furthermore, substitution of Fe over Zn in Metalloporphyrin cage has enhanced the optical nonlinearity. This research effort offers a significant understanding into metal (Fe/Zn) to metal (Mo) charge transfer through imido-linkage in hexamolybdates, which has been found to be an efficient mode to enhance NLO response as a prime example in modulation of optoelectronics.